Developer mixes



United States Patent 'Ofitice 3,3203%? Patented May 16, 1967 3,320,169 DEVELOPER MIXES Robert M. East, Mount Prospect, and John A. Harmon,

Arlington Heights, Ill., assignors to Addressograph-Multigraph Corporation, Mount Prospect, Ill., a corporation of Delaware No Drawing. Filed Aug. 3, 1964, Ser. No. 387,218 Claims. (Cl. 252-621) This invention relates to electrophotographic processes for producing visible records and more particularly to developer mixes for use in such process. This application is a continuation-in-part of application Ser. No. 221,888 filed Sept. 6, 1962, now abandoned.

Known electrophotographic processes involve the production of a negative electrostatic charge on the surface of a photoconductive insulating material containing photoconductive particles such as zinc oxide. A latent light image is produced on this photoconductive surface by exposure to light rays in the image pattern, which light rays effect a discharge of the portions irradiated by the light rays. The latent image is rendered visible by applying thereto a developer powder which is held by electrostatic attraction on the charged areas. The developer powder thus applied is fixed by fusing, solvent treatment or other known procedure.

When produciing a positive copy from a negative original or a negative copy from a positive original, i.e., a reverse copy of an original, a developer mix is employed, the developer powder or toner of which is repelled by the charged areas of the image, usually the background areas, which powder or toner adheres to the discharged areas. Such developer mix is known in the art as a reversal developer mix. When producing a positive copy of the electrostatic image a developer mix is employed, the toner of which adheres to the charged areas, i.e., the toner has a charge of opposite polarity to that of the electrostatic image. Such developer mixes are known as positive developer mixes.

One known technique of applying such reversal and positive developer mixes is the so-called magnetic brush technique involving the use of a mixture of larger mag netic particles, usually iron, and smaller toner or powder particles constituted of pigmented resin and the application of this developer mix by means of a cylindrical magnetic applicator roller on the periphery of which the magnetic brush is formed and reformed during the rotation of the applicator roller to maintain enough toner in the so-called brush for proper development of the image. The image bearing member, usually paper, is passed in substantially tangential contact with this brush with the side to be developed in contact or near contact with the brush and the opposite side, herein termed the back, positioned remote from the magnetic brush. Such type of developer is disclosed, for example, in the Paul B. Streich, Sr., United States Patent No. 3,003,462 granted October 10, 196-1.

Another technique of developing electrostatic latent images involves the application of developer mixes by cascading said mixture over the charged surface. The electroscopic powder which adheres to the carrier particles is attracted by the imaged portions of the electrophotographic member adhering thereto as the carrier particles flow over the image.

Both reversal and positive mixes after use for some time tend to show gradual drop-off in performance. The carrier particles appear to lose their capacity to carry or attract the electroscopic powder. This is an indication of a depreciation of the triboelectric forca between the carrier and toner particles. The carrier particles appear to lose their attractive force toward the electroscopic powder or toner. In some cases this inability to carry or attract the electroscopic pOWder occurs after the formation of only 2,000 to 6,000 prints. The carrier particles in such instances must be replaced in order to restore the developer mix to satisfactory operation.

Evidence of such deterioration appears in the photoelectrostatic copies which begin to show adherence of the electroscopic powder or toner indiscriminately in both image and nonimage areas. For example, copies will show up with increased amounts of background in the nonimage areas.

Another evidence of mix deterioration is a fall-off or loss in copy density, that is, the developed image appears gray rather than having an intense black color. Also, magnetic carrier particles may begin to deposit on the copy sheet as a result of mix deterioration, giving the photoelectrostatic copy a gritty feel.

Deterioration of the developer mixes tends to deposit the toner onto parts of the developer apparatus which comes into contact with the copy paper. In reversal printing, for example, it is customary to maintain a seal or guide member covering the container or trough in which the magnetic applicator roll rotates, with the seal position just above the applicator roll so that the recording member passes beneath the seal with the back of the recording member in substantially frictional contact with the underside of the seal. The latter thus aids in maintaining the image bearing surface of the recording memher in contact or near contact with the magnetic brush. In some electrophotographic machines it is common practice to continually rotate the applicator roll once the machine is turned on even though the recording members are passed intermittently through the developer portion of the machine. As the developer mix begins to deteriorate a developer powder collects on the underside of the seal; upon passage of recording member thereunder some of this powder is deposited on the back of the recording member resulting in the production of prints or copies which have unsightly or messy deposits of toner on the backs thereof.

Presently available developer mixes also have the disadvantage that the toner particles teud to form clouds of fine particles similar to dust which result in soiling the prints and in an objectionable atmosphere in the neighborhood of the developer.

Electroscopic powders tend to concentrate at the edge portions of the latent electrostatic image. In reproducing large, solid print areas, the image will be of proper density at the edges and only partially developed at the image center.

It is a principal object of the present invention to provide developer mixes for use in magnetic brush developers, which mixes minimize, it not completely overcome, the above noted objectionable characteristics of heretofore known developer mixes.

It is another object of this invention to provide developer mixes which when in use result in improved prints, particularly from the standpoint of the clarity and distinctiveness of the prints.

It is another object of this invention to provide a reversal developer mix which when in use results in improved prints, particularly from the standpoint of the cleanliness of the back of the prints.

Other objects and advantages of this invention will be apparent from the following detailed description thereof.

The developer mixes of this invention are three component mixtures consisting essentially of (1) magnetic carrier particles, (2) toner particles having a particle size smaller than the particle size of the magnetic carrier particles, the toner particles consisting essentially of a discrete mixture of pigmented resin particles having the necessary triboelectric relationship to the magnetic carrier particles so that upon admixture the toner particles acquire a charge of the desired polarity to develop the image, and (3) an aliphaic acid having from 10 to 26 carbon atoms and/or a salt of such aliphatic acid, the cation of the salt being calcium, barium, sodium, lithium, magnesium, manganese, zinc, nickel, iron, cobalt, lead or ammonium. A mixture of any two or more of these aliphatic acids and/ or salts can be used. For convenience and brevity the expression additive will be used herein to refer to such aliphatic acid, salt thereof or mixture of such salts, or mixture of such acids, or mixture of such salts and such acids.

The additive can be in the liquid or solid phase depending on whether it is in the liquid or solid phase at the ambient temperature conditions when added to the mix or during mixing. For example, oleic acid is liquid at room temperature and remains in the liquid phase when used as the additive in the mix. The salts of the fatty acids are solid at room temperature and desirably are added in the solid phase. During the mixing, however, particularly in the case of those salts having relatively low melting points, they can be reduced to the molten state, thus insuring thorough mixing with the magnetic carrier particles and the toner.

The magnetic particles can be iron, ferrites, nickel, cobalt, or other magnetic particles having an average particle size of from 25 to 500 microns, preferably 25 to 150 microns, and always larger than that of the toner particles. For reversal developer mixes, the magnetic particles and the toner particles are chosen to have a triboelectric relationship such as to produce a negative charge on the toner particles when the two are mixed. For positive developer mixes, the magnetic particles and toner particles are chosen to have a triboelectric relationship such as to produce a positive charge on the toner particles when the two are mixed.

The toner consists of thermoplastic resins containing suitable pigments and orienting materials. In both the reversal and positive developer mixes, the thermoplastic resin component of the toner can be a polystyrene resin, acrylic resin, wood rosin, asphalt, gilsonite, polyvinyl resin or other such resin employed in the production of electroscopic developer powders. The resins should have a melting point below the char point of paper and preferably a melting point in the range of from 100 to 140 C. The resin should have a reasonably sharp melt point so that in fixing the image, the developer powder is readily converted from discrete, solid particles to a melt.

Pigments or dyes incorporated in the resin for both reversal and positive developer mixes can be carbon black or bone black, where a black developer powder is desired, phthalocyanine, azo, vat and acid dyes which when in corporated in the toner result in toner particles having the resistivity hereinafter disclosed. The amount of pigment or dye incorporated in the resin, in the case of the reversal developer mix, is from 1 to 3 parts per 95 parts of resin, and in the case of the positive developer mix is from 1 to 5 parts per 95 parts of resin. The positive toner has a greater tolerance for the amount of pigment that can be incorporated without adversely affecting the desired triboelectric relationship between it and the magnetic carrier particles.

The orienting material incorporated in the reversal developer mix preferably is a non-crystallizing phthalocyanine green pigment. The amount used is from 1 to 3 parts per 100 parts of resin. For the positive developer mix from 1 to 5 parts per 100 parts of resin of an orienting material such as nigrosine, iosol black or malachite green can be used.

The toner is made by melting the resin, adding the pigment and orienting material to the molten resin and uniformly distributing it in the melt, thereafter solidifying the melt by cooling and grinding the resultant solid toner particles to an average particle size of from 1 to 75 microns, preferably 4 to 10 microns. This particle size is satisfactory for both reversal developer mixes and positive developer mixes. In the case of the reversal developer mix, the resin, pigment or dye and orienting material are chosen to produce a toner having a resistivity in the range of from 10 to 10 ohm-cm. For the positive developer mix these components are chosen to produce a toner having a resistivity below 10 ohm-cm. The upper limit of 10 ohm-cm. for the resistivity of the positive toner is critical. Unless the resistivity of the positive toner is less than 10 ohm-cm, it will not give good copies; the resistivity of the positive toner can have any value below 10 ohm-cm., i.e., can be from 0 to 10 ohm-cm. The examples which follow give typical formulations for both reversal and positive developer mixes.

In making the reversal developer mix of this invention the magnetic carrier particles, the toner particles, as well as the third component, that is, the additive, are combined within specific ranges of proportionality in relation to the amount of carrier particles present. Magnetic carrier particles ranging from 10 to 60 parts by weight having the particle size above disclosed are mixed with each part by weight of toner and for each parts by weight of carrier particles there is included from 0.02 to 0.4 part by Weight of the additive.

In making the positive developer mix from 10 to 100 parts of magnetic carrier particles having the particle size above disclosed are mixed with each part by weight of toner. The range of additive which may be employed is again determined in proportion to the amount of magnetic carrier particles present, it having been found to 100 parts by weight of carrier particles, there should be present in the range of from 0.02 to 0.1 part by weight of the additive.

The additive can be a fatty acid, saturated or unsaturated, containing from 10 to 26 carbon atoms, such, for example, a scapric, lauric, myristic, palmitic, stearic, arachidic, behenic, lignoceric, cerotic, decylenic, stillingic, dodecylenic, palmitoleic, oleic, gadoleic, arachidonic, cetoleic, erucic, and selacholeic, or the calcium, barium, sodium, lithium, magnesium, manganese, zinc, nickel, iron, cobalt, lead and ammonium, salts of any of these fatty acids or a mixture of either these fatty acids, the aforesaid salts thereof, or a mixture of both these fatty acids and these salts. Preferred additives are calcium stearate and lithium stearate. The particle size of the additives in the solid phase should be about one micron or less. It is important that the particle size of the additive in the solid phase be small enough to give reasonably good coating of the magnetic carrier particles when the magnetic carrier particles, toner and additive are mixed in the relative proportions hereina-bove disclosed.

Thorough mixing of the components of both the reversal developer mix and positive developer mix is carried out in any suitable equipment to provide a thorough mixture of the components. The additive appears to coat the magnetic carrier particles providing a protective film or coating which it is believed is responsible in part, at least, for the improved triboelectric characteristics of the developer mix embodying this invention.

It is important that the additive remain either in the liquid phase in the case of those additives incorporated in the liquid phase, or in the case of those additives incorporated in the solid phase as discrete solid particles coating the magnetic carrier particles and toner particles and uniformly distributed throughout the mixture of magnetic carrier particles and the toner particles. Blending of the additive along with the pigment and orienting material with the resin melt followed by solidification of the melt and grinding of the solid particles does not produce a developer mix having the advantageous properties of the developer mix of this invention in which the additive is homogeneously distributed throughout the mixture of magnetic carrier particles and toner particles and forms a coating or a film on the exterior of these particles.

The following examples are given for illustrative purposes. It will be understood this invention is not limited to these examples.

In this specification all parts and percentages are given on a weight basis.

EXAMPLE I Reversal developer mix Carrier: Parts Powdered iron, at least 95% passed through 100 mesh and retained on 200 mesh 500.0 Toner 10.0

5.7 Polystyrene resin, melting point (ring and ball) 100 C.- 3 C. (Piccolastic D400). 3.8 Polystyrene resin, melting point (ring and ball) 125 C.i3 C. (Piccolastic C-125). .3 Carbon black. .2 Green pigment (Heliogen Green, General Aniline & Film Corp). Additive:

Calcium stearate having a particle size of about 1 micron .2

The above toner constituents are incorporated by adding the carbon black and green pigment to the molten blend of resins, mixing until a homogeneous mixture results, cooling to solidify the mix, and then grinding the solidified pigmented resin to a particle size of from 5 to 20' microns.

To this toner powder is added calcium stearate and the powdered iron, and the mixture subjected to agitation to produce a uniform mix constituted of discrete particles of powdered iron, pigmented resin and calcium stearate.

EXAMPLE II Reversal developer mix This example differs from Example I in that barium stearate is used instead of calcium stearate in the same relative proportions.

EXAMPLE III Reversal developer mix In this example lead stearate is used in the same relative proportions as the calcium stearate of Example I.

EXAMPLE IV Reversal developer mix This example differs from Example I in the substitution of magnesium stearate in the same relative proportions for the calcium stearate of Example I.

EXAMPLE V Reversal developer mix This example differs from Example I in the substitution of zinc palmitate for the calcium stearate in Example I; the amount of zinc palmitate is substantially the same as the amount of calcium stearate.

All of the Examples I to V, inclusive, of reversal developer mixes when used in a magnetic brush applicator having a flexible sealing cover extending across the open top of the trough in which is mounted for rotation the applicator roller disclosed, for example, in Paul B. Streich, Sr., application Ser. No. 216,632 filed Aug. 13, 1962, eliminated the unsightly and messy deposits of toner on the backs of prints processed in such equipment. In the operation of the machine the additive is deposited on the underside of the flexible seal, i.e., the side immediately adjacent to the magnetic applicator roller. This resulted in the formation of a charge on the underside of the seal of a polarity opposite to that on the toner of the reversal developer mix, which charge tends to repel the toner.

This minimizes, if not completely prevents the transfer of the toner to the underside of the flexible seal and from g the latter to the prints.

The examples which follow are examples of positive developer mixes. In all of these examples the toner was produced by adding the pigment and orienting the material to molten resin in the proportions indicated, the resultant mixture mixed to obtain uniform distribution of the pigment and orienting material in the molten resin, the mixture then solidified by cooling and grinding to an average particle size of from 4 to 10 microns. These toner particles were then blended with the indicated additive in the indicated proportions. To this mixture was added the indicated amount of magnetic carrier particles.

EXAMPLE VI EXAMPLE VII Positive developer mix Carrier: Parts Powdered iron, passed through mesh 1500.0 Toner 45.03

25.6 Polystyrene-Piccolastic D-l00, Pennsylvania Industrial Chemical Co. 16.6 PolystyrenePiccolastic D-125, Pennsylvania Industrial Chemical Co. 2.2 Nigrosine black. 0.63 Carbon black. Additive:

Lead stearate EXAMPLE VIII Positive developer mix Carrier: Parts Powdered iron, passed through 100 mesh- 1350.0 Toner 45.1

15.7 Polyamide resin, Versamid 930, General Mills Chemical Div. 24.4 Rosen-modified resin, Amberol 800 manufactured by Rohm & Haas. 1.1 Carbon black, Columbian Carbon. 3.9 Black dye, Nigrosine Black, Keystone Aniline & Chemical Co. Additive:

Lithium stearate EXAMPLE IX Positive developer mix This example differed from Example VIII in the substitution of oleic acid for the lithium stearate of Example VIII. 0.3 parts of oleic acid were incorporated in the mix.

EXAMPLE X Positive developer mix This example differed from Example VIII in the substitution of a mixture of oleic acid and stearic acid for the lithium stearate of Example VIII. 0.25 part of the acid mixture were incorporated in the positive developer mix.

EXAMPLE XI Positive developer mix This example differed from Example VIII in the substit-ution of palmitic acid for the lithium stearate of Example VIII. 0.3 part of palmitic acid were incorporated in the mix.

In use as the toner in the mix is used up, additional toner mix with additive is added for replenishing purposes. Such mixture can be free of magnetic particles or, if desired, for replenishing purposes, a mixture containing approximately equal parts of magnetic particles and toner and containing from 0.02 to 0.4 part by weight of additive per 100 parts by weight of carrier in the case of the reversal mix and from 0.02 to 0.1 part by weight of additive per 100 parts by weight of carrier in the case of positive developer mix, can be used.

The developer mixes of this invention generally improve the quality of copies obtained :by dry electrostatic printing processes as compared with heretofore known mixes. In both reversal and positive printing, greater image density is achieved on the copies and .less pick-up of toner in the background or non-image areas. There is less of a tendency for the toner to be thrown out, that is to form dust clouds in the vicinity of the developing apparatus. Reversal prints are free of excessive developer powder clinging to their backs. Prints made with the positive developer mix show markedly less tendency towards development along the edges; large solid print areas are reproduced with good uniformity of color throughout the area.

Moreover, the developer mix has good life, including life in storage without marked deterioration. The additives prevent caking of the developer mixes during shelf storage; the mixes tend to remain in granular free-flowing condition.

The exact explanation of why the fatty acids and the salts thereof, herein disclosed, are effective to correct the problems of prior known developer mixes is not fully understood. The improvement in print density, reduced background and minimization of mix deterioration is believed to be due in part at least to the additive affecting the triboelectric relationship between the carrier and the toner. The additive tends to maintain a proper triboelectric charge balance between the toner and the magnetic carrier particles so that the attraction between the latter and the toner does not override the attractive force of the charged areas of the electrostatic recording member for the toner. In reversal printing, this balance permits the proper repulsion of the toner to effect adherence thereof to the areas of the print to which the developer powder should be applied. In positive printing, this balance enables the charged image areas to attract and hold the toner.

Moreover, the presence of the additive tends to improve the mobility of the components of the developer mixes resulting in better mixing or distribution of the toner relative to the carrier particles, particularly when fresh toner is introduced into the developer mix. With the developer mixes of this invention, the introduction of fresh toner along with additive in proportions of from 0.02 to 0.4 part by weight of additive per 100 parts by weight of carrier in the case of the reversal developer mix, and from 0.02 to 0.1 part by weight of additive per 100 parts by weight of carrier in the case of positive mix results in the more complete and uniform distribution of the fresh toner throughout the developer mix upon subjecting the mixture to agitation or mixing. Such mixing is conventional in the operation of electrostatic printing machines.

As noted, the additive markedly improves the longevity of the developer mix. 10,000 prints have been made with the developer mixes of this invention without the mix showing signs of exhaustion, whereas, under similar conditions, with prior known developers not containing the additive hereinabove disclosed, only from 2,000 to 6,000 prints could be made before replacement of the developer mix became necessary.

It will be understood that this invention is not to be limited to the present disclosure except as indicated in the appended claims.

What is claimed is:

1. A developer mix for developing electrostatic latent images on photoconductive insulating material employing a magnetic brush for applying the developer to the latent images, which developer mix consists essentially of magnetic carrier particles and toner particles having a particle size smaller than the particle size of the magnetic carrier particles, the toner particles consisting essentially of a pigmented thermoplastic resin having a resistivity less than 10 ohm-cm. and a particle size of from 1 to 75 microns, said toner particles being mixed with the magnetic carrier particles having a particle size of from 25 to 150 microns in the proportions of from 10 to parts of magnetic carrier particles per part of toner particles by weight, and said developer mix containing from 0.02 to 0.4 part by weight of a third component per 100 parts by weight of carrier particles, said third component intimately mixed with and forming a coating on the exterior of said magnetic carrier particles and said toner particles, said third component being selected from the group consisting of (a) fatty acids containing from 10 to 26 carbon atoms; (b) a salt of such fatty acids, the cation of the salt being selected from the group consisting of calcium, barium, sodium, lithium, magnesium, manganese, zinc, nickel, iron, cobalt, lead and ammonium; (c) a mixture of said fatty acids; (d) a mixture containing at least one of said fatty acids and at least one of said salts; and (e) a mixture of said salts.

2. A reversal developer mix for developing'electrostatic images on photoconductive insulating material employing a magnetic brush for applying the developer to the latent images, which developer mix consists essentially of a mixture of magnetic carrier particles and toner particles having a particle size smaller than the particle size of the magnetic carrier particles, the toner particles consisting essentially of a pigmented thermoplastic resin having a resistivity in the range of from 10 to 10 ohm-cm. and a particle size of from 1 to 75 microns, said toner particles being mixed with the magnetic carrier particles having a particle size from 25 to microns in the proportions of from 10 to 60 parts of magnetic carrier particles per part of toner particles by weight, and said developer mix containing from 0.02 to 0.4 part by weight of an additive per 100 parts by weight of carrier particles, said additive being intimately mixed with the magnetic carrier particles and toner particles while the latter are in the solid phase to' form a coating of said additive on the magnetic carrier particles and toner particles, said additive being selected from the group consisting of (a) fatty acids containing from'lO to 26 carbon atoms; (b) a salt of said fatty acids, the cations of said salt being selected from the group consisting of calcium, barium, sodium, lithium, magnesium, manganese, zinc, nickel, iron, cobalt, lead and ammonium; (c) a mixture of said fatty acids; ((1) a mixture of at least one of said fatty acids and at least one of said salts; and (e) a mixture of said salts.

3. A reversal developer mix as defined in claim 2 in which the thermoplastic resin is polystyrene pigmented with carbon black and the metal salt is calcium stearate.

4. A reversal developer mix as defined in claim 2 in which the thermoplastic resin is polystyrene pigmented with carbon black and the metal salt is barium stearate.

5. A reversal developer mix as defined in claim 2 in which the thermoplastic resin is polystyrene pigmented with carbon black and the metal salt is lead stearate.

6. A reversal developer mix as defined in claim 2 in which the thermoplastic resin is polystyrene pigmented with carbon black and the metal salt is lithium stearate.

7. A reversal developer mix as defined in claim 2 in which the thermoplastic resin is polystyrene pigmented with carbon black and the metal salt is zinc palmitate.

8. A positive developer mix for developing electrostatic latent images on photoconductive insulating material employing a magnetic brush for applying the developer to the latent images, which developer consists essentially of a mixture of magnetic carrier particles and toner particles having a particle size smaller than the particle size of the magnetic carrier particles, the toner particles consisting essentially of a pigmented thermoplastic resin having a resistivity less than 10 ohm-cm. and a particle size of from 1 to 75 microns, said toner particles being mixed with the magnetic carrier particles having a particle size of from 25 to 150 microns in the proportions of from 10 to 100 parts of magnetic carrier particles per part of toner particles by weight, and said developer mix containing from 0.02 to 0.1 art by weight of an additive per 100 parts by weight of carrier particles, said additive being intimately mixed with the magnetic carrier particles and toner particles while the latter are in the solid phase to form a coating of said additive on the magnetic carrier particles and toner particles, said additive being selected from the group consisting of (a) fatty acids containing from 10 to 26 carbon atoms; (b) a salt of said fatty acids, the cation of said salt being selected from the group consisting of calcium, barium, sodium, lithium, magnesium, manganese, zinc, nickel, iron, cobalt, lead and ammonium; (c) a mixture of said fatty acids; (d) a mixture of at least one of said fatty acids and at least one of said salts; and (e) a mixture of said salts.

9. A positive developer mix consisting essentially of magnetic iron particles having a particle size of from 25 to 150 microns, pigmented thermoplastic resin particles having a resistivity of less than 10 ohm-cm. and a particle size of from 1 to 75 microns, mixed with the magnetic iron particles in the proportions of from 10 to 100 parts of magnetic iron particles per part by weight of said resin particles and containing from 0.02 to 0.1 part of lithium stea rate per 100 parts by weight of carrier intimately mixed in discrete form with the magnetic carrier particles and the resin particles.

10. A positive developer mix consisting essentially of magnetic iron particles having a particle size of from to 150 microns, pigmented thermoplastic resin particles having a resistivity of less than 10 ohm-cm. and a particle size of from 1 to microns, mixed with the magnetic iron particles in the proportions of from 10 to parts of magnetic iron particles per part by weight of said resin particles and containing from 0.02 to 0.1 part of calcium stearate per 100 parts by Weight of carrier intimately mixed in discrete form with the magnetic carrier particles and the resin particles.

References Cited by the Examiner UNITED STATES PATENTS 4/1961 Giaimo 252-62.1 6/1962 Wielicki 1l717.5

JULIUS GREENWALD, I. D. WELSH,

Assistant Examiners.

Attest:

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3,320, 169 May 16, 1967 Robert M. East et a1 pears in the above numbered pat- It is hereby certified that error ap atent should read as ent requiring correction and that the said Letters P corrected below.

Column 8, lines 29 and 30, after "electrostatic" insert latent Signed and sealed this 21st day of November 1967.

(SEAL) EDWARD J. BRENNER Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer 

1. A DEVELOPER MIX FOR DEVELOPING ELECTGROSTATIC LATENT IMAGES ON PHOTOCONDUCTIVE INSULATING MATERIAL EMPLOYING A MAGNETIC BRUSH FOR APPLYING THE DEVELOPER TO THE LATENT IMAGES, WHICH DEVELOPER MIX CONSISTS ESSENTIALLY OF MAGNETIC CARRIER JPARTICLES AND TONER PARTICLES HAVING A PARTICLE SIZE SMALLER THAN THE JPARTICLE SIZE OF THE MAGNETIC CARRIER PARTICLES, THE TONER PARTICLES CONSISTING ESSENTIALLY OF A PIGMENTED THERMOPLASTIC RESIN HAVING A RESISTIVITY LESS THAN 10**19 OHM-CM. AND A PARTICLE SIZE OF FROM 1 TO 75 MICRONS, SAID TONER PARTICLES BEING MIXED WITH THE MAGNETIC CARRIER PARTICLES HAVING A PARTICLE SIZE OF FROM 25 TO 150 MICRONS IN THE PROPORTIONS OF FROM 10 TO 100 PARTS OF MAGNETIC CARRIER PARTICLES PER PART OF TONER PARTICLES BY WEIGHT, AND SAID DEVELOPER MIX CONTAINING FROM 0.02 TO 0.4 PART BY WEIGHT OF A THIRD COMPONENT PER 100 PARTS BY WEIGHT OF CARRIER PARTICLES, SAID THIRD COMPONENT INTIMATELY MIXED WITH AND FORMING A COATING ON THE EXTERIOR OF SAID MAGNETIC CARRIER PLARTICLES AND SAID TONER PARTICLES, SAID THIRD COMPONENT BEING SELECTED FROM THE GROUP CONSISTING OF (A) FATTY ACIDS CONTAINING FROM 10 TO 26 CARBON ATOMS; (B) A SALT OF SUCH FATTY ACIDS, THE CATION OF THE SALT BEING SELECTED FROM THE GROUP CONSISTING OF CALCIUM, BARIUM, SODIUM, LITHIUM, MAGNESIUM, MANGANESE, ZINC, NICKEL, IRON, COBALT, LEAD AND AMMONIUM; (C) A MIXTURE OF SAID FATTY ACIDS; (D) A MIXTURE CONTAINING AT LEAST ONE OF SAID FATTY ACIDS AND AT LEAST ONE OF SAID SALTS; AND (E) A MIXTURE OF SAID SALTS. 